Deleting matrix elements efficiently

Question

I want to efficiently delete a lot of data from the beginning of a matrix of dimension 2*n. The matrix looks like this:

x1 x2
x3 x4
...
...

I

Answer 1

One way is to just compare the entire first column in one go and then delete, i.e.

rows2delete = list{i}(:,1) <= someNumber; %# creates logical array with 1 for deletion
list{i}(rows2delete,:) = []; %# delete some rows, all corresponding cols